The present embodiments relate to medical imaging. Three-dimensional (3D) visualization is a common practice to assess and record the internal conditions of patients. Both anatomical and functional information may be available for visualization. Functional information represents biological activity and is from molecular imaging modalities like positron emission tomography (PET) or single-photon emission computed tomography (SPECT). Anatomical information is available from other modalities, such as computed tomography (CT) or magnetic resonance imaging (MRI).
Conventionally, PET and SPECT information is fused with CT and MRI volume data, showing functional information as colored blobs using a color palette for increased metabolism. The color palette may range from yellow for medium to red for high metabolism. In a conventional ray-casting algorithm, the color emission from voxels of the PET and SPECT data is derived from the intensity of the measured functional activity. When visualizing functional information together with registered anatomical information, the functional information should be clearly visible, showing areas of increased biological activity within the anatomical context. Clear viewing of the functional information might be difficult, since anatomical features often occlude the functional information. For example, a tumor with greater biological activity is embedded in an organ, so the anatomical representation of the organ blocks viewing of the embedded functional information.
The occlusion may be avoided, at least in part. Since the emitted color for the functional information is only transported on a direct path from the emitting point to the image plane pixel in ray casting approaches, the transfer function for the anatomy information is set in a way that bones are opaque while soft tissue is transparent. Alternatively, cut planes are employed to remove occluding anatomy. Both approaches result in less anatomical information.